Document separation/detection technique

ABSTRACT

A method for differentiating and separating multiple overlapped like documents from single like items, transported along track means, comprising: subjecting the documents to opposed vacuum forces from suction means to separate them at a separation-station; then determining whether the documents are single or multiple, by measuring and analyzing the resulting pressure differentials within the suction system; using a cyclonic filter for removing and storing dust and debris entrained within the suction-conducting airflow, the cyclonic filter and suction system being designed and adapted to provide a relatively constant vacuum-generating airflow regardless of the nature of quantity of debris removed; plus a pressure sensor for indicating whether one or several documents are passing.

This is a Division of application Ser. No. 08/197,420, filed Feb. 15,1994, now U.S. Pat. No. 5,419,546 which is a Division of 08/176,368filed Dec. 30, 1993, now U.S. Pat. No. 5,437,395.

FIELD OF INVENTION

This invention relates to document detection systems, and particularlyto those using a vacuum-separation method to identify and signal doubledocuments and employing associated vacuum generating, coupling andsensing means. Particular attention is given to the use of such systemsin high-speed document processing machinery.

BACKGROUND, FEATURES

Workers in the field of high-speed document processing, such as in thesorting of bank checks and like financial instruments, know that the artrequires the use of machines and systems capable of moving andprocessing very large volumes of documents at rates of thousands ofdocuments per minute, while performing multiple and interrelatedoperations upon each document as it travels through such machinery. Suchoperations might include, but are not limited to, printing upon thedocuments, reading data previously encoded thereon by a variety ofprocesses, recording an archival image of the document by photographicor electronic-imaging techniques, and other processes and manipulations.

The "doubles" Problem:

Workers understand that, while processing such large volumes ofdocuments, it is vital that each individual document be transported andprocessed singly, and that documents remain in the order and sequence inwhich they were processed by the machine. To attain the rates ofdocument processing required, the documents are fed and separated fromone another by machinery, which is extensively designed and engineeredto ensure that documents are fed one at a time ("Singly") with a veryhigh degree of reliability. Should two or more documents be accidentallyfed and processed together, extensive manual effort and time arerequired to track down this error among the many thousands of documentswhich the machine may process within a very brief time. For this reason,the most extreme measures are implemented to ensure that the documentfeeding and separating measures always feed documents one at a time, nomatter what their condition.

Nonetheless, there are occasional unavoidable circumstances where themachinery will feed more than one document at a time. Examples aredocuments which are stapled or glued together, documents which adhere toone another due to ink or other surface treatments, or documents whichare attached one another by mutual tears or folds. Such cases are knownin the art as "double-documents" or simply "doubles". Human operatorsfor such sorting and processing machinery are aware that "doubles" are acostly and time-consuming event, and guard against them as far aspossible; still, the sheer volume of documents means that a "double"will occur from time to time.

For this reason, workers find that the machinery itself must contain areliable device for separating and detecting "doubles" as soon aspossible after they have been fed; preferably before much processing isperformed on them. In this way, the operator may be warned of thepresence of a "double" before it can cause a disruption to the normalflow of work (e.g., and remove it).

We have contemplated different techniques for sensing and reporting adouble-document. Such techniques must take account of the widely varyingcharacteristics of the documents (e.g., thickness, density, opacity,etc.), as well as the increasing document speeds which are the result ofcontinuing efforts to increase the processing rate. Theoretically,"doubles" might be sensed optically, mechanically or electronically--asnoted below:

Optical sensing:

By shining a beam of light through the document and measuring how muchof the beam passes through to impinge on a sensor, the additionalthickness of a second document should produce a measurable change insignal.

This technique, while practical in principle, tends to perform poorly inservice. The wide range of characteristics of the documents being fed,especially as regards opacity and thickness, renders such a techniquedifficult to implement in practice. Because such a system must tend tooperate in a "fail-safe" mode, it has to lead to a high incidence offalse "doubles". Such a false report is almost as disruptive as a real"double" would be.

Additionally, optical sensors are very susceptible to failure due to thehigh levels of dust and debris found around document processingmachinery.

Mechanical sensing:

By passing the document between a known reference point and some movingeffector, such as a stylus or roller, the thickness of the document maybe measured by means of one of a variety of sensors. The additionalthickness of a second document should be measurable.

Once again, the wide range of characteristics for documents fed makethis a poor system. The thickest documents may well be more than twicethe thinnest, causing a high incidence of "false doubles". Additionally,the sensors required to detect mechanical variations of this order aresensitive and costly, and require skilled and time-consuming calibrationto give a reliable result.

Electronic sensing, relying on the variation of a parameter such asreluctance or permeability to detect the presence of documents.

Again, the range of document characteristics render such techniques lessthan successful, also they require the use of costly, custom-sensingelements.

Rather, we settled on a vacuumatic separating/sensing technique; andfound it to give high reliability regardless of the nature and conditionof the documents. This invention seeks to teach improvements in suchtechniques to enhance reliability, serviceability and whole-life cost.

Basic Vacuumatic System (FIGS. 1, 1A):

FIGS. 1, 1A, 2 show a basic, simplified version of a vacuum-separationand sensing system of the type we first favored. Here, it will beunderstood that the documents to be sensed are transported in a verticalposition by transport means such as belts, pulleys and the like (notshown, but well understood in the art). The documents d are constrainedto pass through a vacuum-separation manifold M which encloses the lowerlongitudinal edge of the document as it passes.

This manifold incorporates two vacuum ports V1 and V2, each disposed ona respective side of the document. The two ports are connected to acommon plenum chamber P, which is kept at negative pressure relative tothe surrounding atmosphere by vacuum blower means B, (or the like)connected to plenum P by hose means H.

Connected to a port Q provided in the wall of hose means H is adifferential pressure switch S1 which compares the pressure within thehose to the ambient atmospheric pressure.

When no document is present, both vacuum ports V1 and V2 are open andunobscured, and air may freely flow into them under the influence ofblower means B. The pressure differential between the inside of hose Hand the surrounding atmosphere is "LOW"(ΔP_(L)).

When a single document passes through manifold M, it will be pulledtowards one or other of the two vacuum ports V1-V2 by the suctionapplied from blower B; the document will tend to close off whichever ofthe ports it is first drawn to. The other port will remain open andunobstructed. The document will cause some reduction in the airflowthrough ports V and there will be a "Moderate" pressure differential(ΔP_(M)) between the inside of hose H and the surrounding atmosphere.

When two or more documents pass through manifold M side-by-side (or justoverlapping), they will tend to be separated by the suction applied fromblower B and each will tend to be drawn to an adjacent vacuum port V.When one port is closed and blocked by a document, the suction at theother port will be increased by virtue of the restriction of theairflow, so this port will tend to draw-in the second document even morestrongly. When both ports are thus closed and blocked, airflow is veryquickly reduced to almost nil very quickly and the differential pressurebetween the inside of hose H and the surrounding atmosphere will veryquickly rise to the highest level of vacuum (ΔP_(h)) which blower B iscapable of sustaining at this point.

It will thus be seen that, by monitoring the pressure differentialbetween the inside of hose H and the surrounding atmosphere, anindication of the presence of more than one document in manifold M maybe obtained which is more or less independent of any physicalcharacteristic of the documents (such as opacity, thickness, color andso on) and is also independent of the number of documents present. Byselecting a threshold of pressure differential for switch S1 whichcorresponds to "both ports V covered"(e.g., ΔP_(h)), such an arrangementcan automatically indicate "more than one document", regardless of theactual number of documents involved, and regardless of their individualcharacteristics.

The action of switch S1 is converted to an electrical signal, which isprocessed by signal-conditioning circuitry (not shown, but familiar toworkers in the art) and provides to the controlling systems of the(check-sorting) machine an indication that a "double" has been detected.The controlling systems can then direct the suspected "double" to aholding area of the machine, without further processing, and alert themachine operator, who may investigate the item manually to correct orotherwise resolve the "double".

Since such a "doubles-detect" arrangement was first contemplated, therehas been significant progress in the design of check sorting machines.Document speeds and feed rates have increased, and the types and qualityof documents handled have expanded beyond any expectation. Additionally,expectations are now greater; e.g., as to convenience of operation,cleanliness, hygiene, and safety. Modifications have to be made to meetthese needs. Among these conditions are the following:

Re Separation/sense Time:

Increasing document speeds have reduced the time available for a"doubles-detect" system to operate on a passing document and determinewhether it is a "double". As an example, the Unisys DP1800 check sortingmachine operates at a nominal track speed of 300 inches per second (ips,or 7.62 meters per second), and may operate with documents with aminimum length of 5.75 inches (11.4 centimeters). For such a document,the time available to operate on a document (e.g., to separate? ) is5.75/300 seconds, or about 19 milliseconds. Future developments arelikely to increase document speed to as much as 400 ips (10.1 metres persecond), with a corresponding reduction in time available for a sensorto make its determination. To allow a system to operate adequatelywithin such reduced time periods, larger and more powerful blowers (B)have to be employed. A blower for the DP1800 product, for example, wouldbe rated to flow 30 cubic feet of air per minute and provide a maximumvacuum of 30 inches water gauge. These high airflows and vacuums wouldbe required to ensure that the "double" is separated within the manifoldM as quickly and securely as possible, even when the documents consistof heavier paper stock with higher resistance to "bending".

Re Dust:

Increasing document speeds and a wider range of document types lead tomore dust and debris being generated in the machine. This material mayconsist of paper fragments and dust, generated by the friction ofdocument-driving elements or from the cut and sheared edges of the paperitself, as well as rubber and plastic particles shed from the drivingelements (e.g., rolls, belts and the like, as well understood by workersin the art).

Paper handling business machines (e.g., Unisys check processors) employvacuum systems to transport or detect documents or for other functions.The vacuum is generated by vacuum pumps or blowers. These pumps/blowersrequire filtration of the air they move to protect their internal movingcomponents from damage from dust/dirt in the air. Additionally, anyexhaust air must be filtered to prevent contamination of the customer'soffice environment.

Since paper handling machinery usually generate lots of paper dust, thepump/blower air filters tend to quickly fill with dust.

Typically the air filtration systems used are "barrier type" i.e.,fiberglass or porous filter paper of some type. These require frequentfield service maintenance for cleaning or replacement. In a high volumesite for a Unisys DP1800 document processor, these filters typicallyrequire replacement twice a week. This frequent servicing by skilledfield engineers adds substantially to the maintenance cost of this typebusiness machine.

One advantage of a "cyclone" paper dust collector is that it can containrelatively large amounts of dust in its bunker, and so reduce therequired frequency of maintenance. In a DP1800 document processor forexample, using a cyclone filter/blower embodiment can reduce frequencyof service from twice a week to once every 3 months (or 1:24 ratio); andthere are other advantages, such as:

No gradual changing pressure drop with the cyclone as with a barriertype filter.

Quick and easy bunker clean out; simply draw the collected dust out ofthe bunker with a standard vacuum cleaner.

Now, such dust/debris will naturally be drawn into the manifold M of adoubles-detect system under the action of the vacuum generated by blowerB, and it may collect within the system. There, it may clog pipes andhoses, such as the connection to the pressure switch S1, or it may buildup inside the blower B to the point where performance is reduced,requiring extensive maintenance and reducing machine up-time. Finally,such material will be (mostly) ejected from the system in the exhaust ofblower B, into the surrounding atmosphere, where it creates an unsightlyand unhealthy environment for attendants. It can also constitute a firehazard if allowed to accumulate, both inside the machine and in thesurrounding environment.

ΔP as Mini-pulses:

Increasing speeds, and the resulting need for increasing vacuum, havealso led to subtle changes in the way that a system must function andprovide sensing output. The changes in pressure detected by the pressureswitch S1 have become less of a mass-air-flow phenomenon (as they wereat lower speeds and lower airflows) and more of a "pulse" phenomenon.Where document speeds are slower, pressures would rise and fall (inresponse to the states of vacuum ports v) relatively slowly and evenlythroughout the system. With much higher speeds and airflows, and muchshorter transitions at vacuumports V, pressure changes now move throughthe system as a "pulse" of reduced pressure, entrained in a high-speedcolumn of air moving through the system. While this is not a problem inand of itself (since the pressure switch S1 can still detect and respondto such "pulses" in the same way as if they were a more generalreduction in pressure throughout the entire system), precautions have tobe taken to prevent minor, spurious pulses ("mini-pulses", or transientspikes) of changing pressure from being generated and producing falseresults at the pressure switch. To this end, sensing port Q is movedfurther down hose H from manifold M to provide an effective column ofair within hose H between manifold M and sensing port Q. The mass andvolume of this column can act as a dynamic damper for pressurevariations travelling there along, and can attenuate the magnitude ofsuch pulses as they travel from manifold M to sensing port Q. In thisway, the impact of such pulses at pressure switch S1 may be reduced,though not entirely eliminated.

Similar problems from "mini-pulses" can also be caused by the documentsthemselves as they travel through manifold M. As document speedsincrease, aerodynamic effects become more and more significant. Adocument's leading edge may "hunt" from side to side; also the entiredocument may assume one of several conditions, such as an undulationfrom side to side along its length, or a tendency to travel at an angleto the direction it is being driven in. These conditions may, in turn,lead to unexpected results at manifold M, where a single document mayrapidly obscure first one vacuum port V, then the other, setting up aseries of high-frequency pulses in the airflow, in Manifold M and in thevarious hoses connecting it to blower B. Thus, pressure switch S1 mustbe carefully designed and tested to ensure that such mini-pulses do notcause spurious signals. Also, more stringent measures should be taken toselectively damp the airflow to filter out and negate suchmini-pulses.

Adding Filtration (FIG. 2):

FIG. 2 shows modifications in the FIG. 1 arrangement for addressing someor all of foregoing concerns. The system is altered by addition of amechanical air filter F in hose H, and provision for adjusting theairflow through hose H is made by adding a variable orifice R at theentrance to air filter F. The air filter serves to separate dust anddebris from the air stream before it enters blower B, and to prevent itfrom clogging the blower and/or being expelled into the surroundingenvironment. Variable orifice R allows the air flow (and therefore thesystem differential pressures), to be calibrated to a known standard,which is typically measured by applying a vacuum gauge (not shown, butwell known in the art) to a test port T provided in the body of the airfilter housing.

While these measures address the identified system problems, they bringproblems of their own and generate new system problems. The air filter,for instance, will soon become clogged with dust and debris, thustending to restrict airflow and alter the differential pressures withinthe system. As this restriction increases with the buildup of debris,the system will tend to miss doubles, since the vacuum at manifold Mwould be reduced. Thus, a system to warn the operator of excessivebuildup of filtered material is desirable--e.g., consisting of apressure switch S2 which measures the differential pressure across thefilter and warns the operator when it reaches a predetermined level,indicating that the filter is excessively clogged. As speeds increase,the replacement period for filter elements will decrease in proportion,until, in some systems, these filters will need to be replaced every fewdays to maintain consistent system performance.

Also, variations in filter elements etc., will typically make itnecessary to check and adjust system pressures every time the filter ischanged. One can do this with variable orifice R, allowing an attendantto adjust system pressures to a known standard. This practice, whileimproving system performance, and maximizing filter replacementintervals, adds considerably to service time and cost.

All the foregoing conditions combine to produce a set of requirementsfar more stringent than were originally conceived. Since air flow ratesare far higher, the system must be designed with a minimum ofrestrictions which might reduce the flow or produce undesired pressureeffects. Variations in airflow (and therefore pressure) must be kept toa minimum over the long term, to maximize the thresholds defining a"double"and to minimize the incidence of false signals. And the systemmust accommodate a large and continuous supply of dirt and debriswithout impacting its function and (preferably) without ejecting a lotsuch material into a customer's environment.

This invention addresses these and related problems; e.g., teaching adoubles-separation/doubles-detect arrangement using vacuumatic means,teaching such with opposed vacuum-ports and associated pressure-sensingmeans to signal the presence of a single document or overlappeddocuments; preferably by locating such sensing means sufficiently remotefrom such ports to provide a damping-column adequate to attenuate, ormask-out, minor pressure variations; by teaching air-filter means andrelated variable orifice means and filter-pressure-sensing means toadequately filter-out contaminants entrained in the line from such portsto the vacuum source, while also allowing one to be aware of excessacross-filter blockage, and to "re-tune" the system pressures once afilter element is installed/replaced.

And, beyond the foregoing, it is an object hereof to teach such a systemwherein the vacuum manifold and sensing means are integrated into asingle unit of minimal and controlled variability, while the supportingsystems are so designed as to provide optimum airflow over long periodswith minimal maintenance. The taught arrangement also includes afunction whereby the sucking vacuum is kept essentially constant, andwhereby dirt and debris are automatically extracted from the airflow asa function of its operation, but without use of a barrier filter andwith minimal impact upon normal operation, and means whereby suchforeign matter may be accumulated over long periods and purged from thesystem without impact upon its normal operation.

The methods and means discussed herein will be generally understood asconstructed and operating as presently known in the art, except whereotherwise specified; and with all materials, methods, devices andapparatus herein understood as being implemented by known expedientsaccording to present good practice.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of advantage of the present invention will beappreciated by workers as they become better understood by reference tothe following detailed descriptions of past and present preferredembodiments which should be considered in conjunction with theaccompanying drawings, wherein like reference symbols denote likeelements.

FIG. (1) is a simplified schematic view of a "basic" vacuum-separationdoubles-detect system as previously described with FIG. 1A enlarging theseparation manifold thereof;

FIG. (2) is a schematic view showing how the basic system of FIG. (1)can be constructed to include features which attempt to address someshortcomings;

FIG. (3) is a schematic view of the most preferred embodiment of thepresent invention, with features of advantage which address manyshortcomings of the systems of FIGS. (1) and (2);

FIG. (3a) is an enlarged view showing the detail of the manifold of FIG.3;

FIG. (4) shows the general configuration of a Cyclone Filter-Pumpsuitable for the preferred embodiment of FIG. 3 (with FIG. 4A showing adetailed sectional view of the construction, FIG. 4B a section thruentry);

FIG. (5) shows a detail of the construction of a "variable aperture"which preferably forms part of the cyclone filter shown in FIG. (4);while FIGS. 6, 7 show such a filter-pump and FIG. 8 schematicallyindicates a predecessor system.

GENERAL CONCEPT OF PREFERRED EMBODIMENTS

In the text foregoing, the basic technology of thevacuum-separation/doubles-detect arrangement was discussed, withparticular reference to the problems which accompany present use of sucha system and the difficulties we have found as system parameters becamemore demanding.

A more perfected system would address all these various shortcomings,and especially, it would:

filter the air to remove entrained dust and debris but would notradically change the airflow or the differential pressures of thesystem, regardless of the amount of debris removed or the length ofservice time. Such a separation system would preferentially also collectthe removed debris so it could be easily purged with minimalintervention by service personnel;

be constructed so that the pressure switch sensing pressure changescaused by a "double" would be (so far as possible) immune to transientminor pressure pulses and to other effects associated with high-speedtransport of documents; and

include provision for engineered and variable damping of the response ofthe pressure switch to allow the system to be tuned to provide the mostreliable response despite varying document conditions.

DESCRIPTION OF A PREFERRED EMBODIMENT

A most preferred embodiment of the present invention is shownsemi-schematically in FIG. (3).

The vacuum separation of documents, and the pressure effects produced bydifferent combinations of documents, remain unchanged from thatpreviously described, and the configuration of vacuum ports V andmanifold M immediately surrounding them is as previously described.

"at-plenum" sensing port Q:

However, in contrast to previous embodiments, the vacuum manifold M inthe area of plenum P is here redesigned to incorporate a sensing port Qwithin plenum P, placed as close as possible to the two vacuum ports V,but sufficiently far from them that the pressure changes experienced atthe site of said ports are the result of the combined influence of bothvacuum ports V, and are not influenced at any given time by the pressureat one port more than the pressure at the other port. In this manner,changes in pressure, corresponding to different combinations ofdocuments, may be imparted to pressure switch (sensor) S1 as quickly aspossible, and without the intervention of an unduly-long air passageinherent in hose H as in previous embodiments.

In previous embodiments, the length of hose H between plenum P andsensing port Q was to also be used as an "air-column damper" to absorbthe effects of minor undesired pressure pulses as previously described.This application was prone to variation and error due to variations inthe manufacture and assembly of hose H and possible changes in itsconfiguration once in the field. A twist or kink, imparted by a carelesstechnician, could radically alter this damping effect and lead to achange in system performance.

Accordingly, as a feature of advantage, we have removed thisair-column-damping feature and disposed sensing port Q as close aspractical to plenum P, as shown in FIG. (3).

Latch:

As a further feature of advantage, the signal-conditioning electronicswhich process the-signal from pressure switch S1 are additionallyredesigned to provide a variable "latch" feature which further reducesthe number of false signals which the sensor may generate. This "latch"feature (not shown, but well understood in the art) operates so as tosend a "double" signal to the system electronics only after the pressureswitch has continuously indicated the "doubles pressure" condition for apre-determined period of time. In this way, system "noise" generated bybrief minor transient high-pressure pulses (air pressure spikes of veryshort duration, which would be minimally compensated by damping means Dbut might, in an extreme case, be sufficient to activate switch S1) maybe effectively filtered out.

In our preferred embodiment, the "holding time" of this "latch" featureis made adjustable; we have found optimum "holding" time to be the orderof 6.0 milliseconds for the described system-this corresponding topassage of about one third of the length of the shortest permitteddocument at the rated transport speed. We have found 6 ms long enough tofilter out all false signals caused by highly transient pressure pulses(error spikes), while still more than short enough to ensure that all"doubles" are indicated by the system.

"No vacuum" Indicator:

Workers studying this system will realize that there is some (small)inherent risk, that total failure of the vacuum-producing system (e.g.,Blower B goes down) will not be detected by pressure switch S1. In thenormal operating state, pressure switch S1 detects only a pressuredifferential between the immediate area of the manifold M and thesurrounding atmosphere. Should the vacuum-producing system fail entirely(e.g., by a failure of blower B or a blockage of one of theinterconnecting hoses), the pressure inside manifold M and outside itwill become equal and will not alter no matter how many documents passthrough the manifold. In this situation, pressure switch S1 will neverbe activated, and a "double" could be passed.

In order to guard against such a an occurrence, various means can beemployed. A rotation sensor can be added to blower B, to indicate to thedocument processor electronics whether or not the motor is turning. Or aflow sensor can be added to one of the interconnecting hoses, toindicate the presence, and velocity, of the airflow.

We have found, however, that the most preferred method is the use of asecond pressure switch S3, disposed as shown in FIG. (3). This switchresponds to differential pressure between the inside of hose H and thesurrounding atmosphere. Since its only purpose is to indicate thepresence or absence of vacuum in the system, it is preadjusted torespond at a relatively low vacuum level. But this low vacuum level,while providing robust sensing of the presence of a vacuum, also makesthe switch more prone to spurious signals from pulse-type pressurevariations, as previously described.

We could eliminate such errors by means of an electronic "latch" withinthe signal conditioning circuitry, as we have previously described foruse with the doubles-detecting switch S1. However, this introducesadditional components into the electronics and is not really warrantedfor such a relatively simple function. Accordingly, we prefer toeliminate the effects of minor, transient "noise" pulses on pressureswitch S3 by inserting a "mechanical latch" or damper means D in thehose between it and the main hose H, as shown in FIG. (3). This damper,preferably, consists of a cylindrical slug of a sintered particulatemetallic material, of known and stable permeability to air, which servesto delay the incidence of No-vacuum to switch S3, to thereby eliminatethe effects of any such "spike" pressure pulse. The sintered particlesize, density and overall length of damping means D may be optimized toprovide consistent damping for a given set of system parameters, yeteasily modified to allow for changes in system parameters (such as achange in vacuum or airflow) without need to re-engineer the entiresystem.

Since damping means D allows S3 to warn of vacuum loss over a relativelylong time interval (as compared to the relatively brief reaction timefor a "doubles-detect" as with switch Si, or vs. the even briefertransient mini-pulses), we find that a composition of sintered materialwhich has a damping coefficient (time to come to equilibrium followingchange of pressure across it) between 10 and 30 seconds gives the mostconsistent and reliable result. This is more than sufficient to suppressthe briefer "doubles pulse" or error all "spike" effects, yet stillgives adequate warning to the system that vacuum is entirely lost.

Cyclone Blower/Filter:

Air passing from manifold M and plenum P then enters a cycloneblower/filter system C comprising a cyclone blower CB with exhaust, plusa cyclone filter F with bunker bb and inlet section including variableorifice means (rotatable collar rc). Filter F etc. is more completelyshown in FIG. (4) and consists of a vertical cylindrical tube t, closedat its upper end except for a vertical exhaust port x which extends downthrough the closed face of tube t, as shown. The lower end of tube t isconically tapered down to an exit port 8F, below which is disposed aclosed cylindrical bunker cavity bb attached to exit port qF. A purginghose ph is connected to bunker bb and is terminated at its outer end ina purge port pp, which incorporates a self-sealing manually-operableclosure (flap f), as shown in FIG. (3).

Incoming air enters Cyclone Filter F by means of tangential entry porttep, which is fashioned in the upper closed end of tube t and constrainsthe incoming air to enter the filter in a direction tangential to thecylindrical inside wall of tube t. Since its only means of escape is viathe open lower end of exhaust port x, the air will commence to flow in acircular, helical motion down the inside wall of tube t. As the airtravels downward, it encounters the conically tapered section ct of thelower end of tube t; this increases air velocity, while at the same timedrawing air toward the open end of exhaust port x. This combined suddenincrease in air velocity and sudden change in direction, serves toinertially and centrifugally separate out (vs. inward, spiral air-flowdrag) dust and debris particles entrained in the air, these being drivenagainst the conically tapered lower wall ct, and moving down the wall(under gravity) until they enter exit port qF and pass into bunkercavity bb. The use of a cyclonic filter, in general, is known in otherfields, such as the mining and food-processing, to filter (separate)particulate matter from an air stream. In certain cases, guide vanes maybe used to help initiate this desired rotational, inward-spirallingflow.

Variable Aperture (FIG. 5):

The hose portion leading to tangential entry port tep of filter F ispreferably provided with variable aperture means to permit selectibleentry of outside air and so provide an adjustment of the level of vacuum(negative pressure) in hose H, plenum P and in manifold M at vacuumports V. The construction of this variable aperture is shown in detailin FIG. (5). It consists of an entry tube Ft projecting from port tep(Ft having aperture a) and a cylindrical rotatable collar rc which fitsclosely on the outside of said tube Ft and is provided with a secondsimilar aperture e. By rotating said collar rc around the outside ofsaid tube Ft the area of the resultant aperture formed by the overlap ofsaid individual apertures a,e may be infinitely varied from zero to thetotal area of said aperture a.

In this manner, the system may be adjusted to give a known vacuum levelin hose H, plenum P and at vacuum ports V-this being optimally matchedto the velocity of the transported documents, the operation of pressureswitch S1, the vacuum and airflow characteristics of cyclonic filter F,damping means D and any minor variations in the various components. Thisadjustment is preferably performed only once, during the assembly of thesystem, and will thereafter remain unchanged. Once adjusted correctly,the position of collar rc may be fixed (e.g., by means of an integral,circumferential clamp ic).

Bunker (FIG. 3):

With reference to FIG. (3), cylindrical bunker bb is provided with apurge hose ph, which terminates in a purge port pp mounted on theexterior face of the machine in some convenient location. This purgeport is provided with a normally-closed manually-operable door, orsealing flap f, and is fashioned to accept coupling of the suction hoseof a standard vacuum cleaner. In normal operation, purge port pp issealed closed and purge hose ph forms a dead air volume which has noimpact on operation. When it is desired to remove accumulated debrisfrom bunker bb, flap f may be opened and a vacuum cleaner connected topurge port pp and the accumulated material sucked out in a matter ofseconds. Since this may temporarily alter the pressure differentialswithin the system, this procedure should be performed at a convenientopportunity while the system is idle. However, this purge process willhave no impact upon the subsequent operation of the system, and may beperformed at any time, by untrained personnel, and without the need forsubsequent checking or adjustment of the system (e.g., no need toretune, vs when a barrier filter is changed).

This is a tremendous advantage over barrierfilter systems like that inFIG. 2 Our testing has shown that in an identical system running anidentical schedule, where the previous design incorporating an airfilter required replacement of the filter every 2 working days, thispreferred embodiment would perform without significant variation forapproximately 100 days before it was felt necessary to empty the bunker.(a 1:50 improvement.) Moreover, where such a barrier-filter gradually,and continually, degrades vacuum, and must be "retuned" after eachfilter change (with the whole machine DOWN the while--something whichcan be expensive, and is to be avoided ), no significant pressurevariations at all occur with this embodiment.

Exhaust port x of cyclonic filter C is attached to blower means B, andthe exhaust from blower B is ejected from the machine at some suitablepoint.

Constant Vacuum:

It was surprising that such a cyclone filter/blower arrangement coulddeliver adequate suction for the described doubles-detection/-separation(and related sensing), while also providing adequate filtering, and yetdo all this while keeping the suction level almost perfectly constant(for this level of particulate flow). This is especially unexpected inlight of the very small size of the cyclone filter/blower (or vacuumpump) which is preferred. For example, note filter/pump F' adapted forcheck processing apparatus Mmin FIGS. 6, 7. The filter is roughly oneft. high overall and has a bunker bb' of clear plastic so an attendantcan readily "eyeball" how full it is. Bunker bb' has a purge port pp'which is led via purge hose ph to the exterior of apparatus Mm for easyaccess to suction clean-out means. Preferably bb is sized to be filledin several months of average service (e.g., here about 43 cubic in. wasfound suitable). The filter is about 4-5" in diameter (upper cyl.) andhas in-/out-conduits about 1" diameter. The checks are driven pastmanifold M (e.g., by belts) at about 300 in/sec (1800 checks/min) withthe manifold (ports) facing the lower 20-25% of each check. A 30 CFSvacuum pump (B) is found to pull about 30 in. water vacuum, giving a -6to -9 in. water vacuum the plenum with no check present (about -10+in.water for both ports covered). Despite its simplicity and tiny size sucha filter/pump is found quite satisfactory.

Printer Exhaust (FIG. 8):

As an added feature, we prefer to also use such a cyclone filter/blowerfor drawing off excess "ink mist" from the reservoir of an ink jetprinter--where such is used operatively adjacent a "doublesdetect/-separate" unit as aforedescribed--something we were surprised todiscover was readily possible.

Now, at first we used more conventional blower means for both--e.g., asvery schematically indicated in FIG. 8, where one blower B₁ was used tosupport a doubles detector DD, and a second blower B₂ was used to drivethe heads. B₁ could also be used to draw-off the excess ink mist fromabove the ink reservoir 1R of a conventional ink-jet printer (e.g., seeprint-heads h-1, h-2, h-3 h-4). When a cyclone filter/blower array as inFIG. 3 was coupled to also draw-off excess reservoir ink-mist (e.g., seephantom connection iJ in FIG. 3) we were surprised to see how readilythe ink-mist was also disposed of in filter F (e.g., ink droplets dryingand depositing into bunker bb). It will likely be preferred to place achoke ih the line to reservoir 1R to reduce the level of suction,however.

While the foregoing diagrams shown are schematic, it will be understoodby workers in the art that they are intended to show an idealized systemand make no direct reference to pressure drops or variations which mayoccur in the system. Therefore, consistent with known good practice,such a system is preferably constructed with hose and interconnectionmeans kept as short and straight as possible, and with variations in thediameter and section of such means kept to a minimum, in order to keeppressure losses and variations to a minimum, consistent with therequirements of integrating such a system into a check-processingmachine.

CONCLUSION

While vacuum-separation systems are here seen as particularlyadvantageous for use in automated high-speed check sorting machines, asdescribed, workers will readily understand that they have utility forother, analogous applications, such as high-speed currency handling,printing, document-processing and like arts, which require a high-speedmeans for handling and reliably detecting multiple documents or likesheet units carried along a track.

In conclusion, it will be understood that the preferred embodiment(s)described herein are only exemplary, and that the invention is capableof many modifications and variations in construction, arrangement anduse without departing from the spirit of the claims.

The above examples of possible variations of the present invention aremerely illustrative and accordingly, the present invention is to beconsidered as including all possible modifications and variations comingwithin the scope of the inventions as defined by the claims appendedhereto.

What is claimed:
 1. A technique for differentiating and separatingmultiple overlapped like items from single like items, transported alongtrack means, wherein said items are first subjected to opposed vacuumforces from suction means to separate them at a separation-station, andwherein the state of the items, whether single or multiple, is thendetermined; this system being provided with cyclonic filter meansadapted for providing a relatively constant, vacuum-generating airflowregardless of the nature or quantity of any debris removed, if any;wherein said system is provided with pressure sensing means constructedand adapted to indicate whether one or several items are passing saidstation; wherein said pressure sensing means is further provided withvariable damping means both mechanical and electronic; and wherein saidsystem is also provided with fail-safe means to indicate whether saidsuction falls to zero.
 2. A technique for differentiating and separatingmultiple overlapped like items from single like items, transported alongtrack means, wherein said items are first subjected to opposed vacuumforces from suction means to separate them at a separation-station, andwherein the state of the items, whether single or multiple, is thendetermined; this system being provided with cyclonic filter meansadapted for providing a relatively constant, vacuum-generating airflowregardless of the nature or quantity of any debris removed, if any;wherein the cyclonic filter means is further provided with a variableaperture at its input side, said aperture being made adjustable in areafrom zero to a calculated upper limit and serving to admit outside airinto the system and so permit adjustment of airflows, pressures andvacuums within the system.
 3. A method for on-the-fly detection andseparation of multiple like, planar items transported along a track ofan item processor, wherein the items are first subjected to opposedvacuum forces from a suction source, to separate multiple overlappeditems; then measuring and analyzing resulting pressure differentialstaken within the vacuum-forming system; this method including providingcyclonic separator means upstream of the suction source, for helping toprovide constant vacuum-forming airflow regardless of the nature orquantity of any debris to be removed, if any; wherein said cyclonicseparator means is further provided with variable aperture means at itsinput side, said aperture means being made widely adjustable in areafrom zero to a calculated upper limit and serving to admit outside airinto the system and so permit adjustment of airflows, pressures andvacuums within the system.
 4. A method for use in an item processingapparatus, for separating multiple planar items from single like items,these transported along a track wherein the items are first subjected toopposed vacuums to separate them; by a vacuum-generating system; then,their state, whether single or multiple, is determined withpressure-sensing means by measuring and analyzing the resulting pressuredifferentials within said vacuum-generating system; said system, inturn, being provided with cyclonic filter/suction pump means forremoving and storing dust and debris entrained within the vacuum-formingair flow, this cyclonic filter/suction pump means providing a constantvacuum-airflow regardless of the nature or quantity of debris removedand collected; the said vacuum-generating system being also providedwith pressure sensor means to indicate whether single or multiple itemsare passing; and wherein said pressure sensing means is further providedwith variable damping means both mechanical and electronic.
 5. A methodfor separating multiple, possibly-overlapped items transported alongtrack means of an item processing apparatus; wherein said items arefirst subjected to opposed suction forces from a suction systemincluding suction means to separate them at a separation-station, andwherein the state of the items, whether single or multiple, is thendetermined with pressure sensing means by measuring and analyzing theresulting pressure differentials within said suction system; while alsoproviding this system with cyclonic separator means for helping tomaintain a relatively constant vacuum-generating airflow regardless ofthe nature or quantity of debris therein and whether any is to beremoved at all; and wherein said pressure sensing means is furtherprovided with variable damping means both mechanical and electronic. 6.A method for use with an item processing apparatus, for separatingmultiple like items from one another as they are transported along atrack, said method comprising: subjecting the items to opposed vacuumforces from a suction system to separate them; then detecting whetherthey are single or multiple items by measuring and analyzing theresulting pressure differentials within the vacuum-generating suctionsystem with pressure-sensing means;providing suction means to generatesaid vacuum forces, and supplementing this suction means with cyclonicseparator means to help generate said vacuum forces and to help providea constant vacuum-airflow regardless of the nature or quantity of debrisin said airflow or whether any debris is to be removed at all; andwherein said pressure sensing means is further provided with variabledamping means both mechanical and electronic.
 7. A method in a systemdifferentiating and separating multiple overlapped like documents fromsingle like items, transported along track means, this methodcomprising: subjecting said documents to opposed vacuum forces fromsuction means to separate them at a separation-station; then determiningthe state of the documents, whether single or multiple withpressure-sensing means by measuring and analyzing the resulting pressuredifferentials within the suction system; while providing this systemwith cyclonic filter means for removing and storing dust and debrisentrained within the suction-conducting air flow, said cyclonic filtermeans and suction means being designed and adapted to provide arelatively constant vacuum-generating airflow regardless of the natureor quantity of debris removed; said pressure sensing means being furtherprovided with variable damping means both mechanical and electronic.